A classical molecular dynamics study was made of the diffusive motion of benzene molecules on basal planes in the sub-monolayer coverage regime. Atomistic calculations were performed using second-generation and general-purpose force- fields. The former calculations revealed a Brownian nature of the diffusion, with a very small diffusion activation barrier of 11meV; in agreement with the helium and neutron spin-echo spectroscopy data of Fouquet et al. (2006). Reasonable agreement was also found for the general-purpose force-fields if screened charges were used in the description of the Coulombic non-bond interaction. The less computationally intensive general-purpose force-field was shown to give a good qualitative description of the diffusion. A potential energy surface was established for the translational and rotational diffusive motion. This surface revealed a peculiar dependence of the lateral diffusion barriers upon the rotation angle of the benzene molecule, which led to a preferential selection of certain rotational states in the molecular dynamics trajectories.

Molecular Dynamics Simulations of the Diffusion of Benzene Sub-Monolayer Films on Graphite Basal Plane Surfaces. Fouquet, P., Johnson, M.R., Hedgeland, H., Jardine, A.P., Ellis, J., Allison, W.: Carbon, 2009, 47[11], 2627-39